Dale - regarding homebrew crystal filters - I wonder if you or any others
here have looked at Elecraft's crystal filter implementation in the K2?
It's built with discrete crystals and the bandwidth is variable over a large
range. Haven't seen that design exploited elsewhere, but don't know why.
It sure works well.

K8AC

"Floyd Sense" wrote in message
...

Dale - regarding homebrew crystal filters - I wonder if you or any others
here have looked at Elecraft's crystal filter implementation in the K2?
It's built with discrete crystals and the bandwidth is variable over a
large
range. Haven't seen that design exploited elsewhere, but don't know why.
It sure works well.

K8AC

That filter topology was, I think, first used by Ten Tec in their Scout.
From a purist standpoint there can be problems:
1. Asymmetrical skirts
2. Changing IN/OUT Z with BW
3. Shifting center freq as the BW is narrowed ( capacity loading)
4. I am guessing here, but I would think the group delay would suffer at one
end or the other
5. Passband ripple can become excessive as BW is increased.

I looked at this approach, along with a method described in QEX last year
for dealing with the center freq shift, but came to the conclusion that I
could design a much better filter if I optimized each BW- even though it
took 3 filters.

One aspect of filters that has long been either ignored or overlooked (
even though W7ZOI details it in EMRFD) is group delay. A friend (N2PK)
recently sent me 2 WAV files of a Yaesu 1000 stock 250Hz filter and his
homebrew 250 Hz filter. The difference was remarkable- his filter was much
cleaner and crisper sounding, no ringing. Great care was taken with group
delay in his design.

Dale W4OP

It would be interesting to know what was different about his filter. Do you
know?

K8AC

"Dale Parfitt" wrote in message news:3Q03e.27300
snip

One aspect of filters that has long been either ignored or overlooked (
even though W7ZOI details it in EMRFD) is group delay. A friend (N2PK)
recently sent me 2 WAV files of a Yaesu 1000 stock 250Hz filter and his
homebrew 250 Hz filter. The difference was remarkable- his filter was much
cleaner and crisper sounding, no ringing. Great care was taken with group
delay in his design.

Dale W4OP